The present invention relates to micro-processor based electro-pneumatic type locomotive brake control systems and particularly to a pneumatic backup arrangement for such a locomotive brake control system.
Modern day locomotive controls, including the locomotive brake control system, incorporate computer technology to reduce hardware and to facilitate adaptation of the system to various customer requirements.
In one such brake control system, a handle operated, brake command controller outputs a desired brake command signal to a microprocessor unit, which interprets this brake command signal in terms of a feedback signal indicative of the pressure of air in an equalizing reservoir, and then effects operation of application and release electro-magnetic valves to adjust the equalizing reservoir pressure in accordance with the brake command signal.
A high capacity pneumatic relay valve device is employed to vary the trainline brake pipe pressure in accordance with variations of the equalizing reservoir pressure, in order to control the railway car brakes. This so-called brake pipe control circuit of the aforementioned brake control system is shown and described in the U.S. Pat. No. 4,904,027, which is incorporated herein by reference.
The brake control system further includes a locomotive automatic brake control circuit having electro-pneumatic application and release valves and additional electro-pneumatic application and release valves in an independent brake control circuit. The automatic brake control electro-pneumatic valves are operated by the microprocessor in response to changes in brake pipe pressure initiated by the brake pipe control circuit in accordance with movement of an automatic brake handle of the brake command controller. Another high capacity pneumatic relay valve device regulates the pressure in the locomotive brake cylinders according to the pressure output (brake pipe pressure) of the automatic brake control circuit application and release electro-pneumatic valves.
The independent brake application and release electro-pneumatic valves are also controlled via the microprocessor according to movement of an independent brake handle of the brake command controller in a manner similar to operation of the brake pipe control circuit.
A double check valve is provided to direct the higher pressure of the automatic and independent brake control circuits to a high capacity pneumatic relay valve device, which in turn establishes the locomotive brake cylinder pressure.
Such an arrangement makes it possible to not only obtain locomotive braking independently of the train brakes, but also allows the independent locomotive brake to be released without releasing the train brakes, following an automatic brake application.
This latter function, commonly referred to as "bail-off" or "quick release", is obtained by means of a push button operated quick release switch that is preferably located on the independent handle. The switch contact transmits an electrical quick release signal to a quick release electro-pneumatic valve that in turn operates a high capacity pneumatic relay valve that pressurizes the locomotive consist actuating pipe. Pressure switches on the controlling and non-controlling locomotives are operated by the actuating pipe pressure to transmit the quick release signal to the microprocessor unit on the respective controlling and non-controlling locomotives to affect a release of the locomotive consist brakes.
In this aforementioned brake control system, the microprocessor controlled electro-pneumatic valves in the brake pipe control circuit and locomotive automatic brake control circuit are arranged in a fail-safe configuration, the reason being to bring the train to a halt automatically in the event of a microprocessor malfunction. In such a fail-safe configuration, deenergization of the electro-pneumatic valves, due to inability of the microprocessor to produce power at its outputs, results in the locomotive brakes being applied. This holds true on both lead and trail locomotives.
While such a fail-safe brake application is desirable from the standpoint of bringing the train to a stop in the event a loss of power occurs at the microprocessor, it leaves the locomotive engineer vulnerable, in terms of being unaware of such a fail-safe brake application occurring on a trail unit of a locomotive consist. This can result in a dangerous operating condition including dragging brakes which can heat up and damage the locomotive wheels. It will be understood that the automatic brake valve or equivalent electronic brake control means on a trailing unit is cut out, so that no brake pipe pressure reduction and thus no brake application on the lead locomotive and cars of the train is effected as a result of the electro-pneumatic valves in the brake pipe control circuit on the trail unit assuming a fail-safe brake application state.
While the foregoing problem can be solved by simply reversing the configuration of the electro-pneumatic valves in the locomotive automatic brake control circuit, so as to assure a brake release state in the absence of power, this obviously compromises the desideratum of a fail-safe brake application on a lead or controlling locomotive.